1. Field of the Invention
The present invention relates to a method and a tool for at least a portion of a wellbore in a well penetrating a subterranean reservoir, such as for instance an oil and gas reservoir or a water reservoir.
2. Description of the Related Art
After drilling a well, the conventional practice in the oil industry consists in filling the well with a metal lining, a.k.a. casing. The casing is lowered down the hole and cement is pumped inside the casing and returns through the annulus where it is allowed to set. Lining the well aims at a dual purpose: preventing the bore walls from collapsing and isolating the various geological strata and thus, avoiding exchange of fluids between them.
Obviously, a casing cannot be installed once the well is completed, i.e. the production tubing is in place. This can be an issue in particular with so-called horizontal wells often left uncased to maximize production but that, as they age, could benefit from a casing to allow local treatments. Before the completion, it is also obvious that the maximum external diameter of any casing portion has to be smaller that the internal diameter of any previous casing section.
Even though the casing is made of a series of pipes connected end to end thanks to threading portions, in general, several sections of casing are required for lining a well. Indeed, during the entire drilling operation, the well is filled with a drilling fluid or mud. The mud cools the drilling tool and keeps the drilling debris in suspension to enable it to be evacuated to the surface. Another essential function of the mud is to ensure the safety of the well by providing hydrostatic pressure, which is higher than the pore pressure of the formation, thus preventing any inadvertent upflow of gas or other fluids. This pore pressure generally increases with the depth. On the other hand, this hydrostatic pressure cannot be so high that it fractures the rock. So, when the drilled section exceeds a certain length (or more precisely when the depth between the top and bottom exceeds a certain value), the upper part of the well has to be lined to allow the use of mud of higher densities to balance the pore pressure of the bottom part without fracturing the top portion of the well.
Since the well has to be cased starting from the surface, each series of casing must go through the casing already cemented, leading to telescopic pattern with a narrow section. Even though the depth pressure gradient is taken into account when designing a well, additional sections may be required for instance if the well intercepts poorly consolidated formations. If too many sections are needed, the bottom section may become too narrow for the drilling means, the completion equipment or production equipment.
U.S. Pat. No. 5,348,095 discloses a completion method including the use of casing of a ductile material that is plastically deformed to an enlarged diameter with a radial expander. Advantageously, this tube is continuous and thus, can be cemented. On the other hand, the expansion (up to 25%) is accompanied by shrinkage of the total length, leading to problems at the tube ends. Moreover, the load required for the expansion is very high.
To avoid excessive loads during the expansion and the length shrinkage, it has been proposed to use a liner with longitudinal slots as disclosed for instance in U.S. Pat. No. 5,667,011. The liner can be expanded with an expansion mandrel. During the expansion, the slots deform thereby maintaining a constant length. On the other hand, the openings prevent a conventional cementing placement with the settable fluid displaced downwards inside the casing and upwards outside the casing. When cementing is desirable, a full borehole is filled with cement and once the cement is set everywhere, the borehole is re-drilled. The cement may be harder to drill than the subterranean formation and this drilling may damage the liner. Moreover, the expansion rate remains limited and thus, this type of expandable casing cannot be run through production tubings due to their small inside diameter.
Another approach disclosed in U.S. Pat. No. 6,533,036 consists in reinforcing the wall with a cement coating without providing a casing. U.S. Pat. No. 6,533,036 proposes a tool including an injection module connected to a downhole reservoir for storing an activator and pumping from the surface a base fluid that is projected to the wall simultaneously with the activator to activate setting of the base fluid. A slip formwork, located near the activator is used to contain the cement until it sets. This technique requires the use of special cements, such as aluminate cement that cannot be mixed with regular cement, even in small quantities, and consequently raises logistic issues.
Hence it remains the need for alternative completion methods that would overcome some of the drawbacks above-mentioned. It would thus be desirable to have techniques available for at least temporarily treating critical zones, such as poorly consolidated geological layers, to limit the duration and cost of interruptions to drilling, and to do so with no substantial reduction in the hole diameter.